Thermionic emission device having thermal expansion compensating means

ABSTRACT

In a thermionic emission device for use in an electron gun assembly of a cathode ray tube, the thermionic emission device is comprised by a pair of conductive supporting members extending through an insulator substrate and a cathode member supported by the supporting members. The cathode member comprises a flat heater coated with thermion emissive substance and a pair of lead members extending in a direction perpendicular to the plane of the heater and connected between the heater and the supporting members.

United States Patent [1 Mitobe et al.

[ June 4, 1974 THERMIONIC EMISSION DEVICE HAVING THERMAL EXPANSION COMPENSATING MEANS [75] Inventors: Koichi Mitobe; Katsuo Abe, both of Mobara, Japan [73] Assignee: Hitachi Ltd., Tokyo, Japan [22] Filed: Mar. 5, 1973 [21] Appl. No.: 338,366

[30] Foreign Application Priority Data Mar. 22, 1972 Japan 47-33118 [52] US. Cl. 313/345, 313/346 R [51] Int. Cl ..H0lj1/l6,HO1j 19/10 [58] Field of Search 313/332, 341, 345, 346 R,

[56] References Cited UNITED STATES PATENTS 3,405,307 10/1968 Pawlikowski et a1. 313/345 FOREIGN PATENTS OR APPLICATIONS 1,348,046 11/1963 France 313/341 Primary Examiner-Archie R. Borchelt Assistant ExaminerWm. H. Punter Attorney, Agent, or Firm-Chittick, Thompson & Pfund [5 7] ABSTRACT in a thermionic emission device for use in an electron gun assembly of a cathode ray tube, the thermionic emission device is comprised by a pair of conductive supporting members extending through an insulator substrate and a cathode member supported by the supporting members. The cathode member comprises a flat heater coated with thermion emissive substance and a pair of lead members extending in a direction perpendicular to the plane of the heater and connected between the heater and the supporting mem bers.

5 Claims, 9 Drawing Figures THERMIONIC EMISSION DEVICE HAVING THERMAL EXPANSION COMPENSATING MEANS BACKGROUND OF THE INVENTION This invention relates to an electron tube and more particularly to a direct heated type thermionic emission device utilized in an electron gun assembly of a cathode ray tube particularly a television receiver picture tube.

Thermionic emission devices utilized in an electron gun assembly of a cathode ray tube for use in a television receiver are classified into two, one the so-called direct heated type, and the other indirect heated type. FIGS. 1 and 2 of the accompanying drawing show typical constructions of the prior art direct heated type thermionic emission devices.

In the construction shown in FIG. 1, two L shaped electrically conductive supporting members 1 and 1a are secured to an insulative substrate, not shown, andan electric heating element 3 having a flat top 2 and two arcuate side legs is secured, as by welding, to the horizontal legs of'the supporting members 1 and la. A thermion emissive member 4 is welded to the flat top 2 of the heating element 2. The thermion emissive member 4 is heated by passing current through heating element 3 via supporting members 1 and 1'. By this heating, the heating element 3 undergoes thermal expansion in a direction shown by arrows A, which is in alignment with the direction of travel of theelectron beam. Since an electron beam collector (not shown) is located close to the thermionic emission device in alignment with the direction of the electron beam, when the heating element 3 expands in this manner, it will come closer to the control grid (not shown) of the electron beam collector, thus decreasing the spacing between the thermionic emission device 4 and the control grid. In an extreme case the thermionic emission device will come into contact with the control grid which results in an instability of the cut-off characteristic of the cathode ray tube and hence damage of the heating element caused by the high voltage impressed upon the control grid.

FIG. 2 shows an improved construction of the thermionic emission device which was proposed to eliminate the above described movement of the thermionic emission device utilized in an electron gun assembly of a cathode ray tube. In the construction shown in FIG. 2, the lower ends of two rod shaped electric conductive supporting members 6 and 6a are secured to an insulative substrate (not shown) and a flat heating element 5 is supported on the upper ends of the supporting members 6 and 6a via spring members 7 and 7a extending at substantially right angles with respect to the axes of the supporting members 6 and 6a. A thermion emissive member 4 is secured to the heating element 5 at the center thereof. With this construction, since the opposite ends of the heating element 5 is supported by the supporting members through spring members 7 and 7a, the heating member 5 can expand and contract in the longitudinal direction thereof as shown by arrows B. For this reason, it is possible to maintain the spacing between the control grid of the electron beam collector and the thermion emissive member 4 at a constant value irrespective of the thermal expansion of the heating element 5. However, as it is necessary to maintain the heating element 5 in a horizontal plane by means of spring elements 7 and 7a, in order to absorb the longitudinal elongation of the heating element, it is necessary to make large the spacing between stationary supporting members 6 and 6a. This increases the heat capacity of the thermionic emission device.

Further, as the thermion emissive member 4 is welded to the heating element 5, where the thickness of the heating element 5 is minimized for the purpose of increasing the speed of emission of the ,thermions, decreasing the heater power and decreasing as far as possible the heat capacity of the heating element, when subjected to external shocks or vibrations, the thermionic emission device tends to vibrate thus causing microphonic noises which result in stripes on the fluorescent screen of the picture tube, and when the conditions of welding the thermion emissive member 4 to the heating element 5 are not uniform the heat conductivity between these two elements will vary from-one to the other of the products thereby varying the heat capacity of the heating elements.

SUMMARY OF THE INVENTION Accordingly, it is an object of this invention to provide an improved thermionic emission device which can prevent the thermion emissive member from approaching or contacting the control grid due to the thermal expansion of the heating element, which can resist vibration or mechanical shock and which is simple in construction and can be fabricated readily.

.Another object of this invention is to provide an improved thermionic emission device having a definite cut-off characteristic and a stable heater capacity and. can effectively prevent microphonic noises when incorporated into a cathode ray tube.

Briefly stated, in accordance with this invention, there is provided a direct heated type thermionic emission device for use in an electron gun assembly of a cathode ray tube including the electron gun assembly and an electron beam collector, the thermionic emission device comprising an insulator substrate, a pair of electric conductive supporting members extending through the insulator substrate, and a cathode member,

the cathode member including a flat heater coated with thermion emissive substance and extending substantially in parallel with the insulative substrate and a pair of lead members extending in a direction perpendicular to the plane of the heater, one of the ends of the lead members being connected to the heating member at opposite points and the other ends being connected to the upper ends of the supporting members.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:

FIGS. 1 and 2 show typical constructions of two prior art thermionic emission devices;

FIG. 3 is a sectional view of the novel thermionic emission device embodying the invention and combined with the control grid of an electron beam collector;

FIG. 4A shows a plan view of the thermionic emission device of this invention shown in FIG. 3;

FIG. 4B shows a sectional view of the thermionic emission device taken along a line 48-48 in FIG. 4A;

FIG. 5 shows a perspective view of the heating element of the thermionic emission device embodying the invention; and

FIGS. 6A, 6B and 6C show perspective views of another embodiments of the heating element.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A thermionic emission device 8 shown in FIG. 3 is fabricated on a circular insulator substrate 12 having a perforation 11 at its center. Electric conductive supporting members 13 and 13a with their upper ends bent into L shaped configurations penetrate through the substrate 12. A heating element or a cathode member is mounted on the upper ends of a pair of electrically conductive supporting members 13 and 13a to be supported substantially in parallel with the insulator substrate 12. The heating element 10 is made of a nickel-tungsten-zirconium alloy, for example. As shown in FIGS. 4A and 5, the heating element 10 comprises a cylindrical cup shaped heater l4 and a pair of lead members and 15a integral with the heating element and extending tangentially from diametrically opposite points on the periphery of the cup shaped heating member 14. In this example the lead members are formed by cutting the vertical side of the cup shaped heater 14. Thermion emissive substance (not shown) is coated on the upper surface of the heater 14 to form a thermionic emission surface. The outer ends of the lead members 15 and 15a are welded to the upper ends of the supporting members 13 and 13a so that the upper surface of heater l4 lies in parallel with the insulator substrate 12.

When the heater 14 is heated by passing current through supporting members 13 and 13a and lead members 15 and 15a, lead members expand much more than the heater 14 due to thermal expansion.

However, as the lead members 15 and 150 are connected to the cylindrical'heater 14 at diametrically opposite points, their elongation in the direction of arrow C will cause the heater 14 to rotate in the direction of arrow D so that the spacing between the thermionic emissive surface on the upper surface of the heater l4 and the control grid 9 of the collector is maintained constant regardless of the thermal expansion of lead members 15 and 15a. For this reason, it is possible to prevent variation in the cut-off characteristic. Furthermore, it is possible to dispose the thermionic emission surface more close to the control grid 9 than in prior art constructions, so that it is possible to manufacture a cathode ray tube whose second control grid can be operated at a low voltage of only 50 V.

Moreover, as the thermion emissive surface is formed by coating thermion emissive material on the heater 14 it is possible to prevent variation in the heater rating caused by the variation in the welding conditions which has been unaboidable in the prior art construction where the thermion emissive members are welded to the heating elements.

Further, even when the lead members 15 and 15a are designed to have the same dimensions as the spring members 7 and 7a shown inFlG. 2, as the width of lead members extends at right angles with respect to the plane of the heater 14 it is possible to increase the mechanical strength of the lead members by the well known principle of dynamics. Accordingly, it is possible to increase the resistance against mechanical shocks or vibrations applied from outside of the tube, thus preventing microphonic noises caused by such shocks or vibrations.

In a modified embodiment of the heating element shown in FIG. 6A, instead of using a cup-shaped heater 14 shown in FIG. 5, a disc shaped heater 14 is used, and the inner ends of the lead members 15 and 15a are connected to the periphery of the disc shaped heater 14 over a certain length. This construction decreases the heat capacity of the cathode member and simplifies its construction. Again the width of the lead members 15 and 15a extends in a direction perpendicular to the plane of the heater 14, so that it is also possible to in crease the mechanical strength.

In still another modifications shown in FIGS. 68 or 6C, the heater 14 is shaped as a diamond or square, and the lead members 15 and 15a are connected to opposite sides. It can be readily noted that these modified embodiments can also provide the same advantageous merits as the foregoing embodiments.

As above described, the invention provides improved direct heated type thermionic emission devices having simple construction and can prevent variations in the cut-off characteristic and heater rating as well as microphonic noises. The novel direct heated type thermionic emission device is useful in the fabrication of cathode ray tubes of high stability and improved operating characteristics.

What is claimed is:

l. A direct heated type thermionic emission device for use in an electron gun assembly of a cathode ray tube including a thermionic electron generator member and an electron beam collector, said thermionic emission device comprising an insulator substrate, a pair of electric conductive supporting members extending through said insulator substrate, and a cathode member, said cathode member including a flat heater coated with thermion emissive substance and extending substantially in parallel with said insulator substrate, and a pair of flat lead members having their width dimension extending in a direction perpendicular to the plane of said heater, one end of each said lead member being integrally connected to said heating member at opposed points and the other ends being connected respectively to the upper ends of said supporting members.

2. The thermionic emission device according to claim 1 wherein said heater comprises a circular disc and said lead members are connected to said circular disc at diametrically opposite points.

3. The thermionic emission device according to claim 1 wherein said heater takes the form of a diamond.

4. The thermionic emission device according to claim I wherein said heater takes the form of a rectangle.

5. The thermionic emission device according to claim I wherein said thermionic emission device is contained in a cylindrical control grid of a collector of the cathode ray tube. 

1. A direct heated type thermionic emission device for use in an electron gun assembly of a cathode ray tube including a thermionic electron generator member and an electron beam collector, said thermionic emission device comprising an insulator substrate, a pair of electric conductive supporting members extending through said insulator substrate, and a cathode member, said cathode member including a flat heater coated with thermion emissive substance and extending substantially in parallel with said insulator substrate, and a pair of flat lead members having their width dimension extending in a direction perpendicular to the plane of said heater, one end of each said lead member being integrally connected to said heating member at opposed points and the other ends being connected respectively to the upper ends of said supporting members.
 2. The thermionic emission device according to claim 1 wherein said heater comprises a circular disc and said lead members are connected to said circular disc at diametrically opposite points.
 3. The thermionic emission device according to claim 1 wherein said heater takes the form of a diamond.
 4. The thermionic emission device according to claim 1 wherein said heater takes the form of a rectangle.
 5. The thermionic emission device according to claim 1 wherein said thermionic emission device is contained in a cylindrical control grid of a collector of the cathode ray tube. 